Method of performing actions related to handover by a mobile station that is in power saving mode in a wireless mobile communication system

ABSTRACT

A method of performing actions related to handover by a mobile station (MS) in a wireless mobile communication system is disclosed. More specifically, the MS receives information from a base station (BS), wherein the information includes at least one action for performing handover and at least one condition corresponding to the at least one action. Furthermore, the MS transmits a request message to perform the at least one action based on the received information from the BS and receives a response message in response to the request message. Lastly, the MS performs the at least one action according to the received response message.

This application claims the benefit of Korean Application No.P10-2005-0049097, filed on Jun. 9, 2005, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a performing action related tohandover, and more particularly, to a method of performing actionsrelated to handover by a mobile station (MS) that is in power savingmode in a wireless mobile communication system.

2. Discussion of the Related Art

In a broadband wireless access system, a power saving mode or a sleepmode can be used to minimize power consumption of a mobile station (MS).The power saving mode comprises a sleep interval and a listeninginterval, which are repeated during the operation by the MS. A length(or duration) of the sleep interval is determined by a value of a sleepwindow. Similarly, a length (or duration) of the listening interval isdetermined by a value of a listening window. These values arerespectively determined based on a characteristic of a determinedtraffic of a corresponding MS. Furthermore, the MS can be represented bythree (3) types of power saving class according to the characteristicsof traffic associated with the power saving class.

More specifically, the three power saving class types are classified asa power saving mode class type 1 (hereinafter “Class 1”), a power savingmode class type 2 (hereinafter “Class 2”), and a power saving mode classtype 3 (hereinafter “Class 3”).

Class 1 can be defined by an initial sleep window, a final window base,a final window exponent, a listening window, and a start frame number ofsleep window. Furthermore, Class 1 focuses on features such as BestEffort (BE) which characterizes the existing interne traffic ornon-real-time variable rate (nrt-VR).

Class 2 can be defined by an initial sleep window, a listening window,and a start frame number of sleep window. Furthermore, Class 2 focuseson features such as Voice over Internet Protocol (VoIP) and the nrt-VR.

Class 3 can be defined by a final window base, a final window exponent,and a start frame number of sleep window. Furthermore, Class 3 is forperiodically transmitting a management message, such as a DownlinkChannel Descriptor/Uplink Channel Descriptor (DCD/UCD) and a neighboradvertisement (MOB_NBR_ADV), to the MS that is in power saving mode oralternatively, for data transmitted via multicast transmission.

The above power saving class types describe different types of powersaving modes. The operations of these different class types are thebasis for handover for the MS to a base station (BS). While in powersaving mode, the MS receives signal quality information of neighbor basestations. The signal qualities of neighbor bases stations can bemeasured by performing scan operation. Before handover operation isperformed, a serving BS transmits handover trigger information, which isused in performing handover, to the MS. Here, the serving BS refers tothe BS which granted the MS to enter the power saving mode. Using thereceived handover trigger information, the MS performs handover when thecondition specified in the handover trigger information is satisfied.

Even if the MS that is in power saving mode does not transmit andreceive a scan request message and a scan response message,respectively, the MS performs scan operation on neighboring basestations and measures signal qualities of neighbor base stations. If theresults of the scan operation (e.g., signal qualities of the neighborbase stations, the received signal strength, and/or transmission delay)are transmitted via scan report message to the serving BS every time thescan operation is performed, the power consumption for uplinktransmission by the MS increases. At the same time, if the serving BSfails to receive the scan results from the MS operating in power savingmode, then the handover operation of the MS cannot be controlledproperly.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method of performingactions related to handover by a mobile station (MS) that is in powersaving mode in a wireless mobile communication system that substantiallyobviates one or more problems due to limitations and disadvantages ofthe related art.

An object of the present invention is to provide a method of performingactions related to handover by a mobile station (MS) that is in powersaving mode in a wireless mobile communication system.

Another object of the present invention is to provide a method ofproviding actions related to handover by a base station (BS) for amobile station (MS) that is in power saving mode in a wireless mobilecommunication system.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod of performing actions related to handover by a mobile station(MS) includes the MS which receives information from a base station(BS), wherein the information includes at least one action forperforming handover and at least one condition corresponding to the atleast one action. Furthermore, the MS transmits a request message toperform the at least one action based on the received information fromthe BS and receives a response message in response to the requestmessage. Lastly, the MS performs the at least one action according tothe received response message.

In another aspect of the present invention, a method of providingactions related to handover by a base station (BS) for a mobile station(MS) that is in power saving mode includes the MS which transmitsinformation to the MS, wherein the information includes at least oneaction for performing handover and at least one condition correspondingto the at least one action. Thereafter, the MS receives a requestmessage from the MS asking to perform at least one action based on thereceived information and transmits response message in response to therequest message.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings;

FIG. 1 is an exemplary diagram illustrating processes of a Power SavingClass 1;

FIG. 2 is an exemplary diagram illustrating processes of a Power SavingClass 2;

FIG. 3 is an exemplary diagram illustrating processes of a Power SavingClass 3;

FIG. 4 is another exemplary diagram illustrating processes of a PowerSaving Class 3;

FIG. 5 shows an example of power saving modes of the MS illustratingvarious service types;

FIG. 6 is an exemplary diagram illustrating handover processes by theMS;

FIG. 7 illustrates an example of an operation of a power saving modewhen the action for transmitting MOB_SCAN-REPORT is enabled;

FIG. 8 illustrates an example of an operation of a power saving modewhen the action for transmitting handover request message (MOB_MSHO-REQ)is enabled;

FIG. 9 illustrates an example of an operation of a power saving modewhen the action for performing scan operation is enabled; and

FIG. 10 illustrates an example of an operation of a power saving modewhen the action for performing association is enabled.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

As discussed above, there are three (3) types of power saving modes. Forproper execution of each power saving mode, the BS and the MS exchangesnecessary information such as parameters and a ranging response(RNG-RSP) message. The parameters are included in the exchanged messagesbetween the BS and the MS. These messages can be defined by a sleeprequest (MOB_SLP-REQ) message, a sleep response (MOB_SLP-RSP) message,and a traffic indication (MOB_TRF-IND) message, for example.

Table 1 illustrates an example of the sleep request (MOB_SLP-REQ)message. The sleep request (MOB_SLP-REQ) message includes a request forentry into sleep mode and is one of the messages transmitted by the MSto the serving BS. In the sleep request message, information pertainingto sleep interval(s) and listening interval(s) can be included.Hereinafter, a term ‘sleep interval’ can be used interchangeably withterms ‘sleep window’ or ‘duration of sleep window.’

TABLE 1 Syntax Size Notes MOB_SLP-REQ_Message_Format( ){  Managementmessage type = 51 8 bits  for(i=0; i<Number_of_Classes;i++){   Operation1 bit   Power Saving Class ID 6 bits   If(Operation=1){   Start_frame_number 6 bits    TRF-IND_Required 1 bit    Reserved 2bits    }   If(Definition=1){    Power Saving Class Type 2 bits   Direction 2 bits    initial-sleep window 8 bits    listening window 8bits    final-sleep window base 10 bits    final-sleep window exponent 3bits    Number of CIDs 3 bits    for(i=0;i<Number_of_CIDs;i++){    CID16 bits    }  }  }

Table 2 illustrates an example of the sleep response (MOB_SLP-RSP)message. The sleep response (MOB_SLP-RSP) message includes sleep moderelated information and is one of the messages transmitted from the BSto the MS. The sleep response message includes grant of sleep mode alongwith sleep interval(s), listening interval(s), and sleep identification,for example.

TABLE 2 Syntax Size Notes MOB_SLP-RSP_Message_Format( ){  Managementmessage type = 51 8 bits  for(i=0; i<Number_of_Classes;i++){  Definition 1 bit   Operation 1 bit   Power Saving Class ID 6 bits  If(Operation=1){    Start_frame_number 6 bits    TRF-IND_Required 1bit    Reserved 1 bit    }   if(Definition=1){    Power Saving ClassType 2 bits    Direction 2 bits    initial-sleep window 8 bits   listening window 8 bits    final-sleep window base 10 bits   final-sleep window exponent 3 bits    SLPID 10 bits    Reserved 2bits    Number of CIDs 3 bits    for(i=0;i<Number_of_CIDs;i++){    CID16 bits    }   }  If(SHO or FBSS capability enabled){ 1 bit   MaintainActive Set and Anchor BS ID   If(Active Set and Anchor BS ID maintained)3 bits    SHO/FBSS duration(s)    }   }   Padding Variable If needed  }

Table 3 is an example of the traffic indication (MOB_TRF-IND) messagebroadcasted periodically. The MS that is in sleep mode receives thebroadcasted traffic indication (MOB_TRF-IND) message during thelistening interval and determines whether to maintain the sleep mode,exit the sleep mode to receive downlink data, or perform rangingoperation during the sleep mode.

TABLE 3 Syntax Size Notes MOB_TRF- IND_Message_Format( ){  Managementmessage type = 52 8 bits  FMT 1 bit 0 = SLPID based format 1 = CID basedformat if(FMT==0)  reserved 7 bits  SLPID Group Indication bit-map 32bits Nth bit of SLPID-Group indication bit-map [MSB corresponds to N =0] is allocated to SLPID Group that includes MSSs with SLPID values fromN * 32 to N * 32 + 31 Meaning of this bit 0: There is no traffic for allthe 32 MSSs which belong to the SLPID-Group 1: There is traffic for atleast one MSS in SLPID-Group  Traffic Indication Bitmap Variable TrafficIndication bit map comprises the multiples of 32-bit long TrafficIndication unit. A Traffic Indication unit for 32 SLPIDs is added toMOB_TRF-IND message whenever its SLPID Group is set to ‘1’ 32 bits ofTraffic Indication Unit (starting from MSB) are allocated to MSSs in theascending order of their SLPID values. 0: Negative indication 0:Negative indication 1: Positive indication  } else {  Num-pos 7 bitsNumber of CIDs on the positive indication list  for{i=0;i<Num-pos;i++){  Short Basic CID 12 bits 12 least significant bits of the Basic CID  } while(!(byte_boundary)){   padding bits <==7 bits padding for bytealignment  }  } }

Table 4 illustrates an example of power saving class parameters includedin the ranging response (RNG-RSP) message. The power saving classparameters can have variable lengths. That is, the power saving classparameters can be defined as a specific type parameter (e.g., type 21)and can be classified as a compound parameter which can selectivelyinclude parameters having varying lengths.

TABLE 4 Name Type Length Value(Variable-length)Power_Saving_Class_Parameters 21 Variable Compound TLV to specify PowerSaving Class Operation Flags 1 bit Bit 0: Definition 1 = Definition ofPower Saving Class present Bit 1: Operation 1 = Activation of PowerSaving Class 0 = Deactivation of Power Saving Class (for type 1 and 2only) Bit 2: TRF-IND_Required For Power Saving Class Type 1 only. 1 = BSshall transmit at least one TRF-IND message during each listening windowof the Power Saving Class. This bit shall be set to 0 for another types.1 = BS shall transmit at least one TRF-IND message during each listeningwindow of the Power Saving Class. This bit shall be set to 0 for anothertypes. Bit 3-7: reserved Power Saving Class ID 1 bit Assigned PowerSaving Class identifier Power Saving Class Type 1 bit Power Saving ClassType Start frame number 1 bit Start frame number first sleep windowinitial-sleep window 1 bit initial-sleep window listening window 1 bitAssigned Duration of MS listening interval (measured in frames)final-sleep window base 1 bit Assigned final value for the sleepinterval(measured in frames)-base final-sleep window exponent 1 bitAssigned final value for the sleep interval(measured in frames)-exponent SLPID 1 bit A number assigned by the BS whenever an MS isinstructed to enter sleep-mode CID CID of connection to be included intothe Power Saving Class. There may be several TLVs of this type in asingle compound Power Saving Class Parameters TLV Direction 1 bitDirection for management connection which is added to Power Saving Class

The operation of the MS prior to handover is as follows. First, the MScan perform scan operation. The scan operation allows the MS to acquiresignals of the neighbor base stations and measure the signal qualitiesof the acquired signals to determine the BS having optimum signalquality among the measured signals. To this end, the MS can use a scanrequest (MOB_SCN-REQ) message to request a serving BS for permission toperform scan operation. In response to the request, the serving BS cansend a scan response (MOB_SCN-RSP) message to allow the MS commence scanoperation of neighbor base stations to measure signal qualities. In thescan response message, parameters needed for performing scan operation,such as for scan period, can be included.

Table 5 illustrates an example of a scan report (MOB_SCAN-REPORT)message.

TABLE 5 Size Syntax (bits) Notes MOB_SCAN- — — REPORT_Message_Format( ){  Management Message Type = 60 8 —  Report Mode 12  0b00: reserved0b01: Report due to: end of “scan report period” 0b10: Report due to:event trigger, using metrics from DCD or MOB_NBR-ADV 0b11: reserved reserved 5 Shall be set to zero  Comp_NBR_BSID_IND 1 —  if(Comp_NBR_BSID_IND == 1){ — —   Configuration Change Count for 8Configuration Change Count value of MOB_NBR_ADV referring MOB_NBR_ADVmessage  } — —  N_current_BSs 3 When FBSS/SHO is supported,N_current_BSs is the number of BSs currently in the active set; whenFBSS/SHO is not supported or the MS has an empty active set,N_current_BSs is set to 1 (=serving/anchor BS).  Reserved 35  Shall beset to zero  For (j=0; j<N_current_BSs; j++) { — —   Temp BSID 4 Activeset member ID assigned to this BS. When the MS has an empty active setor FBSS/SHO is not supported, Temp BSID shall be set to 0.   Reserved 4Shall be set to zero   BS CINR mean 8 —   BS RSSI mean 8 —   Relativedelay / BS RTD 8 When FBSS/SHO is supported, this field will include therelative delay of BSs currently in the active set (Anchor BS relativedelay = 0); when FBSS/SHO is not supported, this field will include theRTD of the serving BS.  } — —  N_NEIGHBORS 8 —  For (i=0; i<N_NEIGHBORS;i++) { — —   If (Comp_NBR_BSID_IND == — — 1){    Neighbor BS index 8 —  } — —   Else{ — —    Neighbor BSID 24  The least significant 24 bitsof the Neighbor BSID   } — —   BS CINR mean 8 —   BS RSSI mean 8 —  Relative delay 8 —  } — — TLV encoded information variable Optional }— —

In operation, the MS can use the scan report message, such as the one ofTable 5, to transmit information (e.g., signal quality, strength ofreceived signal, transmission delay) acquired from the scan operation ofthe neighbor base stations to the serving BS. The serving BS determineswhether to allow MS to perform handover based on information of neighborBS scanned results.

A time it takes to perform handover can be shortened by performingassociation. Association relates to a process or a procedure beforeperforming actual handover. In detail, the MS can first measure signalquality of neighbor base stations via scan operation and execute initialranging operation. Here, the ranging parameters used during the initialranging operation can be re-used during actual handover. Morespecifically, the MS can send the scan request (MOB_SCN-REQ) message tothe serving BS to request for connection with the neighbor BS. Theserving BS in response can provide parameters (e.g., connectionexecution time, resource information used at connection) necessary forconnecting with the neighbor BS via the scan response (MOB_SCN-RSP)message.

As discussed above, the MS can measure signal qualities of the neighborbase stations by using the scan operation and reports the results of thescan operation, including the measured signal qualities, to the servingBS. Thereafter, the MS compares, using an absolute or relative standard,levels of signal qualities that can be provided by the neighbor basestations to level of the actual signal qualities received from theneighbor base stations. After completing the comparison, the MS and/orthe serving BS can determine whether to perform handover.

Conditions or values necessary for the MS to perform various operationscan be transmitted with specified parameters, as illustrated in Table 6.Here, the parameters can include information related to operations suchas scanning the neighbor base stations, reporting the results of thescan operation, connecting with the neighbor BS, and performing handoverwith the BS. These specified parameters can then be included in aDownlink Channel Descriptor (DCD) of the serving BS or a neighbor BSadvertisement (MOB_NBR-ADV) message, and thereafter, transmitted to theMS from the serving BS.

Table 6 illustrates an example of values of a parameter used to triggerdifferent events.

TABLE 6 Type PHY Name (1 byte) Length Value scope CINR trigger 54 3Carrier-to-interference-plus- noise ratio is measured RSSI trigger 55 3Received signal strength is measured RTD trigger 56 3 Round-trip-time ismeasured

Table 7 illustrates an example of conditions of a parameter used totrigger different events.

TABLE 7 Name Type Length Value Function 54.1.1 4 bits Computationdefining trigger condition 55.1.1 (MSB) 0x0: reserved 56.1.1 0x1: Metricof neighbor BS is greater than absolute value 0x2: Metric of neighbor BSis less than absolute value 0x3: Metric of neighbor BS is greater thanserving BS metric by relative value 0x4: Metric of neighbor BS is lessthan serving BS metric by relative value 0x5: Metric of serving BSgreater than absolute value 0x6: Metric of serving BS less than absolutevalue 0x7-0x15: reserved Note: 0x1-0x4 not applicable for RTD triggermetric Action 54.1.2 4 bits Action performed upon reaching 55.1.2 (LSB)trigger condition 56.1.2 0x0: reserved 0x1: Respond on trigger withMOB_SCAN-REPORT 0x2: Respond on trigger with MOB_MSHO-REQ 0x3: Ontrigger, MS starts neighbor BS scan process by sending MOB_SCAN-REQ 0x4:Respond on trigger with MOB_SCN-REQ to perform association 0x5-0x15:reserved Note: 0x3 is not applicable when neighbor BS metric aredefined.

FIG. 1 is an exemplary diagram illustrating processes of a Power SavingClass 1. In the Power Saving Class 1 of FIG. 1, the MS sends a messageto the BS to request for entry into power saving mode, and the powersaving mode is maintained until there is downlink traffic to deliver tothe corresponding MS, at which point, the power saving mode isterminated. A more detailed description of the operation is providedbelow.

In detail, the MS sets the values of initial sleep window, final sleepwindow, and listening window. These values are then included in thesleep request (MOB-SLP-REQ) message transmitted to the BS to request forentry into power saving mode. When or if the BS grants entry into thepower saving mode, the BS includes, inter alia, an initial sleep window,a final sleep window, a listening window, and a start frame of theinitial sleep window in the response message (i.e., MOB-SLP-RSP) to thecorresponding MS.

When the MS enters the power saving mode, the MS remains in the powersaving mode for duration equaling duration of the initial sleep window.After the expiration of the power saving mode, the MS receives trafficindication (MOB-TRF-IND) message(s) from the BS during the listeninginterval. If there is no downlink traffic or data directed to thecorresponding MS, referred to as negative indication, for example, thenthe MS re-enters power saving mode. However, this time, the duration ofthe power saving mode is twice longer than the previous duration.

If there continues to be no downlink traffic for the corresponding MSduring the listening interval(s), then the duration of the subsequentpower saving mode increases by a specified rate (i.e., two folds) eachtime the MS re-enters the power saving mode after failing to receivedownlink traffic after the listening interval. The following equation isan example illustrating increase in duration of the power saving mode.Here, a size or duration of a final sleep window can be determined usinga final sleep window base and a final window exponent included in thesleep response message.

Final Sleep Window=Final Sleep Window Base*2 Final WindowExponent  [Equation 1]

On the contrary, if there is downlink traffic addressed to the MS duringthe listening interval, indicated as positive indication, then the MSterminates the power saving mode.

FIG. 2 is an exemplary diagram illustrating processes of a Power SavingClass 2. In FIG. 2, the diagram shows the MS using any one of anUnsolicited Grant Service (UGS), which provides a fixed data rate, and aReal Time Variable Service (RT-VR), and the operation processes of theMS in a Power Saving Class 2.

More specifically, the MS transmits a sleep request message, similar tothe message of Table 1, to the BS to request for entry to Power SavingClass 2. Upon receipt of the request message, the BS grants entry toPower Saving Class 2 by sending a response message to the MS. Theresponse message can include a sleep interval, a listening interval, anda start frame of the power saving mode to be configured by the MS. Oncethe MS enters the start frame, the MS stays in the power saving mode forthe duration of the sleep interval.

After the sleep interval expires, the MS synchronizes with the BS tomaintain uplink/downlink communication. The MS can then receive downlinkdata from the BS and at the same time, transmit uplink data to the BSduring the listening interval. Once the listening interval ends, the MSmaintains the power saving mode for a period equaling that of the sleepinterval in order to minimize power consumption. Thereafter, thelistening and sleep intervals are repeated by the MS in Power SavingClass 2.

If the MS wishes to terminate Power Saving Class 2, the MS can send asleep request message, including a request to terminate Power SavingClass 2, to the BS during the listening interval. Alternatively, the MScan transmit a user data to the BS during the sleep interval. AfterPower Saving Class 2 is terminated, the MS is in normal operating mode.

FIG. 3 is an exemplary diagram illustrating processes of a Power SavingClass 3. More specifically, FIG. 3 shows the processes of Power SavingClass 3 by illustrating the MS maintaining uplink/downlink communicationwith the BS and performing ranging operations with the BS to reducepower consumption. In FIG. 3, the MS enters normal operation mode bypowering on and executing network entry procedure. During normal mode,the MS performs ranging operations periodically to maintainuplink/downlink communication with the BS. In the process of periodicranging operations, the MS acquires appropriate uplink transmissionparameters. Furthermore, when it is time for the MS to perform periodicranging operations, the MS transmits a ranging request (RNG-REQ) messageto the BS.

After receiving the ranging request message (RNG-REQ) from the MS, theBS responds by transmitting a ranging response (RNG-RSP) message, whichincludes adjusted values of the uplink transmission parameters, to thecorresponding MS. Here, the ranging response message can include sleepwindow and start frame, for example, so that Power Saving Class 3 can beactivated.

After the MS receives the ranging response (RNG-RSP) message, whichincludes information necessary to activate powering saving mode, the MSencounters the start frame to indicate start of the power saving mode.Thereafter, the MS stays in the power saving mode for the duration ofthe sleep window. When the sleep window period expires, the MS is in amode which allows the MS to communicate with the BS. The MS thenperforms periodic ranging operation. During the ranging operation, theMS receives from the BS the ranging response (RNG-RSP) message includingthe parameters related to uplink transmission and power saving mode.When it is time to enter power saving mode, the MS enters (or activates)the power saving mode and remains in the power saving mode for theduration of the sleep window.

FIG. 4 is another exemplary diagram illustrating processes of a PowerSaving Class 3. FIG. 4 depicts the processes of Power Saving Class 3employed by the MS, which receives data from the BS via multicastconnection, to conserve power.

The BS transmits a sleep response (MOB_SLP-RSP) message to the MS tohave the MS activate Power Saving Class 3. When the MS receives thesleep response (MOB_SLP-RSP) message, starting with the start frame, theMS enters or activates the sleep window and remains in the power savingmode for the duration of the sleep window. At the termination of thesleep window, the MS resumes a mode in which the MS is available tocommunicate with the BS, and the MS receives data from the BS viamulticast connection.

After the BS finishes transmitting data during multicast connection, theBS activates Power Saving Class 3 by transmitting a sleep response(MOB_SLP-RSP) message to the MS so that the power consumption can bereduced until the next data transmission via multicast connection. Asfor the MS, the MS responds to the sleep response (MOB_SLP-RSP) messageby entering the power saving mode for the duration of the sleep window.In order to reduce power consumption of the MS in the broadband wirelessaccess system, each connection may be associated with an individualcontext or power saving class according to service type of theconnection.

FIG. 5 shows an example of power saving modes of the MS illustratingvarious service types. As illustrated in FIG. 5, the MS that has atleast one power saving class activated remains in the power saving modeduring sleep windows where the sleep windows overlap between each powersaving class. As described above, the MS does not perform uplinktransmission with the BS during power saving mode.

As described above, the MS and the serving BS activates the power savingmode based on each connection represented by a service type. As such,the MS can minimize power consumption. Alternatively, the MS, evenduring power saving mode, can perform pre-handover operations beforehandover, such as scan operation which detects signal quality levelsreceived from neighbor base stations, and association procedures whichexecutes ranging operations with the BS prior to performing actualhandover, during the sleep window.

The serving BS transmits handover trigger information, which includesoperations such as scan, association, and handover, to the MS. As forthe MS, the MS performs necessary and appropriate operations when thesituation satisfies the condition based on the received handover triggerinformation.

FIG. 6 is an exemplary diagram illustrating handover processes by theMS. In FIG. 6, the serving BS transmits handover trigger information byusing the DCD, which is a message used to transmit channel informationparameters, or a neighbor advertisement (MOB_NBR-ADV) message. Asdescribed above, the handover trigger information includes informationnecessary for the MS to carry out handover operation.

After the MS receives the handover trigger information from the servingBS, the MS can send a scan request (MOB_SCN-REQ) message to requestassignment of scan period (or duration) from the serving BS when thecondition is met to perform scan on neighbor base stations.

After receiving the scan request message, the serving BS allocates thescan period (or duration) included in the scan response (MOB_SCN-RSP)message. During the scan period, the MS synchronizes downlink signalwith the neighbor BS and measures signal quality, signal strength, andtransmission synchronization, among others.

After the MS completes scan, if the MS has to send the scan result ofneighbor base stations to the serving BS, the MS uses the scan report(MOB_SCAN-REPORT) message. More specifically, the scan report includesinformation such as a Carrier-to-Interference and Noise Ratio (CINR), aReceived Signal Strength Indicator (RSSI), and a Round Trip Delay.

If the MS has to perform association with the neighbor BS, the MS cantransmit a scan request (MOB-SCN-REQ) message to request associationwith the neighbor BS to the serving BS. In response, the serving BStransmits via a scan response (MOB-SCN-RSP) message parameters necessaryfor performing association with the neighbor BS. After receiving thenecessary parameters, the MS performs association with the neighbor BS.

After the MS performs scan or association operations, if the MS has toperform handover operation with a particular BS after referring to ahandover trigger information, the MS can use a handover request(MOB_MSHO-REQ) message to request for handover to the serving BS. Uponreceipt, the serving BS transmits a handover response (MOB_MSHO-RSP)message to the MS. Thereafter, the MS transmits a handover indication(MOB_HO-IND) message to the serving BS to request to cease or severconnection with the serving BS. Then, the MS performs operations forre-entry to target BS and the network.

Table 8 is an example of a sleep request (MOB_SLP-REQ) message.

TABLE 8 Size Syntax (bits) Notes MOB_SLP-REQ_Message_Format( ) { ? ?Management message type = 51 8 ? Number of Classes 8 Number of powersaving classes. for (i=0; i< Number of Classes; i++) { ? ? Definition 1? Operation 1 ? Power_Saving_Class_ID 6 ? if (Operation = 1) { ? ?Start_frame_number 6 ? Reserved 2 ? } ? ? if (Definition = 1) { ? ?Power_Saving_Class_Type 2 ? Direction 2 ?Traffic_triggered_wakening_flag 1 ? reserved 3 ? initial-sleep window 68 ? listening-window 4 ? final-sleep window base 10 ? final-sleep windowexponent 3 ? Number_of_Sleep_CIDs 3 ? for (1=0; i<Number_of_Sleep_CIDs;? ? i++ { CID 16 ? } ? ? } ? ? Enabled-Trigger 4 bits Bit #0: Respond ontrigger with MOB_SCAN- REPORT Bit #1: Respond on trigger with MOB_MSHO-REQ Bit #2: On trigger, MS starts neighbor BS scan process by sendingMOB_SCAN- REQ Bit #3: Respond on trigger with MOB_SCN-REQ to performassociation ) TLV encoded information variable ? } ? ?

If the MS wishes to convert to or enter power saving mode, the MS canmake a request for entry to power saving mode by transmitting the sleeprequest (MOB_SLP-REQ) message. Here, the sleep request (MOB_SLP-REQ)message can include information related to whether the MS that is in thepower saving mode should perform each handover-related operations forhandover trigger information.

The information related to whether the MS that is in the power savingmode should perform each handover-related operations for handovertrigger information can be transmitted via a specified field of thesleep request (MOB_SLP-REQ) message. Table 9 is an example of thespecified field, labeled as ‘Enabled-Trigger’ field, of the sleeprequest (MOB_SLP-REQ) message. In detail, Table 9 describes an exampleof a parameter for enabling the event trigger operation.

TABLE 9 Name Type Length Value Enabled- mm 1 byte Indicates actionperformed upon reaching Trigger trigger condition in Sleep Mode If bit#0is set to 1, respond on trigger with MOB_SCAN-REPORT If bit#1 is set to1, respond on trigger with MOB_MSHO-REQ If bit#2 is set to 1, ontrigger, MS starts neighboring BS scan process by sending MOB_SCN-REQ Ifbit#3 is set to 1, respond on trigger with MOB_SCN-REQ to performassociation bit#4-bit#7: reserved. Shall be set to 0.

The parameter of Table 9 is a Type Length Value (TLV) parameter, whichcan be transmitted to the BS via a sleep request (MOB_SLP-REQ) messageor a ranging request (RNG-REQ) message. More specifically, theparameters of Table 9 can be used to negotiate whether each event isenabled or disabled when the MS enters the power saving mode.Furthermore, the parameters of Table 9 can be included in sleep request(MOB_SLP-REQ), sleep response (MOB_SLP-RSP), ranging request (RNG-REQ),and ranging response (RNG-RSP) messages.

The Enabled-Trigger parameter can be in a bitmap format. TheEnabled-Trigger parameter in the bitmap format can be used to notify theserving BS that the corresponding event is to be triggered by the MS. Inoperation, the MS can configure each bit as ‘1’ (e.g., bit=1), andtransmit the configure bit(s) to the serving BS via the sleep request(MOB_SLP-REQ) message. Based on the handover trigger information, if theevent trigger condition is satisfied with respect to the eventconfigured to ‘1’ during the power saving mode of the MS, then theserving BS can be notified that the MS is to trigger the correspondingevent.

If the serving BS receives the sleep request (MOB_SLP-REQ) messageincluding the enabled-trigger parameter, the serving BS can configurethe Enabled-Trigger parameter, as illustrated in Table 9, and cantransmit the configured information to the MS via the sleep response(MOB_SLP-RSP) message. Alternatively, the sleep response (MOB_SLP-RSP)message can include the Enabled-Trigger parameter configured accordingto Table 10.

Table 10 is an example of a sleep response (MOB_SLP-RSP) message.

TABLE 10 Size Syntax (bits) Notes MOB_SLP-RSP_Message_Format( ) { — —Management message type = 51 8 — Number of Classes 8 Number of powersaving classes. for (i = 0; i < Number_of_Classes; — — i++){ Length ofData 8 — Definition 1 — Operation 1 — Power_Saving_Class_ID 6 — if(Operation = 1) { — — Start_frame_number 6 — Reserved 2 — } else { ? —REQ-duration 8 — } — — if (Definition = 1) { — — Power_Saving_Class_Type2 — Direction 2 — if (Sleep-approved == 0) { — — REQ-duration 8 — } ? —initial-sleep window 8 — listening window 8 — final-sleep window base 10— final-sleep window exponent 3 — TRF-IND required 1 —Traffic_triggered_wakening_flag 1 — Reserved 1 — if(TRF-IND required) {— — SLPID 10 — Reserved 2 — } — — Number_of_CIDs 4 — for (i = 0; i <Number_of_CIDs; i++) { — — CID 16 — } — — if (SHO or FBSS capabilityenabled) { — — Maintain Active Set and Anchor BS 1 — ID BSID if(Maintained Active Set and Anchor — — BS ID BSID) { SHO/FBSS duration(s)— — } — — } — — Enabled-Trigger 4 bits Bit #0: Respond on trigger withMOB_SCAN- REPORT Bit #1: Respond on trigger with MOB_MSHO- REQ Bit #2:On trigger, MS starts neighbor BS scan process by sending MOB_SCAN- REQBit #3: Respond on trigger with MOB_SCN- REQ to perform association } —— Padding variable If needed for alignment to byte boundary if(Operation = 1) { — — Power Saving Class TLV encoded — — information } —— } — — TLV encoded information — — } — —

The Enabled-Trigger parameter included in the sleep response(MOB_SLP-RSP) message is in a bitmap format, as in the case with thesleep request (MOB_SLP-REQ) message. Similarly, if each bitmap is set to‘1,’ and if the trigger condition is satisfied based on the handovertrigger information similar to that of Table 7 during power saving modeof the MS, the serving BS notifies the MS to instruct the MS to triggerthe corresponding event.

FIG. 7 illustrates an example of an operation of a power saving modewhen the action for transmitting MOB_SCAN-REPORT is enabled. Morespecifically, FIG. 7 describes operations related to handover of the MSbased on handover trigger information during the operation of MS powersaving mode initiated according to the Enabled-Trigger parameter.

In FIG. 7, the MS receives the handover trigger information via the DCDmessage or the MOB_NBR-ADV message. When making a request for entry topower saving mode, the MS sets or configures a first bit (i.e., bit #0)of the Enabled-Trigger parameter to ‘1,’ as illustrated in Tables 8 and9. Here, setting the first bit of the Enabled-Trigger parameter meansthat the action for transmitting MOB_SCAN-REPORT is enabled. Thereafter,the configured information is transmitted to the serving BS via thesleep request (MOB_SLP-REQ) message.

The serving BS then sets (or configures) the first bit (i.e., bit#0) ofthe Enabled-Trigger parameter to ‘1,’ as illustrated in Tables 9 and 10,and transmits the configured information to the MS via the sleepresponse (MOB_SLP-RSP) message. After receiving the sleep response(MOB_SLP-RSP) message from the serving BS, the MS enters the powersaving mode.

The MS which is in power saving mode can perform scan operations onneighbor base stations during the sleep interval or for the duration ofthe sleep window. When the MS satisfies a condition after entering thepower saving mode, then the MS is required to report the scan result.Thereafter, the MS transmits the scan report (MOB_SCAN-REPORT) messageto the serving BS to provide the serving BS with the scan resultrelating to the neighbor base stations. After reporting the scan resultsto the serving BS, the MS can then maintain the power saving mode.

FIG. 8 illustrates an example of an operation of a power saving modewhen the action for transmitting handover request message (MOB_MSHO-REQ)is enabled. As illustrate in FIG. 8, the MS receives the handovertrigger information via the DCD message or the MOB_NBR-ADV message. Whenthe MS makes a request for entry to power saving mode, the MS sets orconfigures a second bit (i.e., bit #1) of the Enabled-Trigger parameterto ‘1,’ as illustrated in Tables 9 and 10. Here, setting the second bitof the Enabled-Trigger parameter means that the action for transmittingMOB_MSHO-REQ is enabled. Thereafter, the configured information istransmitted to the serving BS via the sleep request (MOB_SLP-REQ)message.

The serving BS then sets (or configures) the second bit (i.e., bit#1) ofthe Enabled-Trigger parameter to ‘1,’ as illustrated in Tables 9 and 10,and transmits the configured information to the MS via the sleepresponse (MOB_SLP-RSP) message. After receiving the sleep responsemessage from the serving BS, the MS enters the power saving mode.

The MS which is in power saving mode can perform neighbor BS scanoperations during the sleep interval or for the duration of the sleepwindow. When the MS satisfies a condition after entering the powersaving mode, the MS is required to report the scan result to the servingBS. Thereafter, the MS terminates the power saving mode and transmitsthe handover request (MOB_MSHO-REQ) message to the serving BS, therebymaking a request for handover with a different BS (e.g., BS2). Inresponse to the handover request (MOB_MSHO-REQ) message, the serving BStransmits a handover response (MOB_MSHO-RSP) message to the MS.

Thereafter, the MS requests for disconnect with the serving BS bytransmitting a handover indication (MOB_HO-IND) message to the servingBS. After the disconnect, the MS performs necessary operations for entryto the target BS (i.e., BS2) and to the network.

FIG. 9 illustrates an example of an operation of a power saving modewhen the action for requesting a scanning interval is enabled. In FIG.9, the MS receives the handover trigger information via the DCD messageor the MOB_NBR-ADV message. When the MS makes a request to enter powersaving mode, the MS sets or configures a third bit (i.e., bit #2) of theEnabled-Trigger parameter to ‘1,’ as illustrated in Tables 8 and 9.Here, setting the third bit of the Enabled-Trigger parameter means thatthe action for requesting MOB_SCN-REQ is enabled. Thereafter, theconfigured information is transmitted to the serving BS via the sleeprequest (MOB_SLP-REQ) message.

The serving BS then sets (or configures) the third bit (i.e., bit#2) ofthe Enabled-Trigger parameter to ‘1,’ as illustrated in Tables 9 and 10,and transmits the configured information to the MS via the sleepresponse (MOB_SLP-RSP) message. After receiving the sleep responsemessage from the serving BS, the MS enters power saving mode.

When the MS satisfies a condition after entering the power saving mode,the MS is required to perform neighbor BS scan operation after.Thereafter, the MS transmits a scan request (MOB_SCN-REQ) message to theserving BS to request for allocation of scan period. In response to thescan request (MOB_SCN-REQ) message, the serving BS transmits a scanresponse (MOB_SCN-RSP) message including allocation of the scan period.

During the scan period, the MS synchronizes downlink signal with theneighbor base stations and measures, inter alia, signal quality fromneighbor base stations, signal strengths, and transmission delay. Afterperforming the scan operation, the MS maintains the power saving mode.

FIG. 10 illustrates an example of an operation of a power saving modewhen the event for performing association is enabled. In FIG. 10, the MSreceives the handover trigger information via the DCD message or theMOB_NBR-ADV message. When the MS makes a request for entry to powersaving mode, the MS sets or configures a fourth bit (i.e., bit #3) ofthe Enabled-Trigger parameter to ‘1,’ as illustrated in Tables 8 and 9.Here, setting the fourth bit of the Enabled-Trigger parameter means thatthe action for performing association is enabled. Thereafter, theconfigured information is transmitted to the serving BS via the sleeprequest (MOB_SLP-REQ) message.

The serving BS then sets (or configures) the fourth bit (i.e., bit#3) ofthe Enabled-Trigger parameter to ‘1,’ as illustrated in Tables 9 and 10,and transmits the configured information to the MS via the sleepresponse (MOB_SLP-RSP) message. After receiving the sleep responsemessage from the serving BS, the MS enters power saving mode. Here, theMS that is in the power saving mode can perform neighbor BS scanoperation during sleep mode.

When the MS satisfies a condition after entering the power saving mode,the MS is required to perform association with a neighbor BS (i.e.,BS2). Thereafter, the MS transmits the scan request (MOB_SCN-REQ)message to the serving BS to request to perform association with theneighbor BS (i.e., BS2). In response to the scan request (MOB_SCN-REQ)message, the serving BS transmits necessary parameters for performingassociation with the neighbor BS (i.e., BS2) via the scan response(MOB_SCN-RSP) message. Thereafter, the MS synchronizes inuplink/downlink directions with the neighbor BS (i.e., BS2) in order toperform association.

Further, the MS transmits a ranging request (RNG-REQ) message to theneighbor BS (i.e., BS2). In response, the neighbor BS (i.e., BS2)transmits ranging control parameters along with association parametersto the MS via a ranging response (RNG-RSP) message. As a feature, the MSkeeps the association parameters received from the neighbor BS (i.e.,BS2) and in turn, can re-use the association parameters when performinghandover with the corresponding BS. After receiving the ranging response(RNG-RSP) message, the MS maintains power saving mode.

As discussed above, the handover operation and related events performedby the MS that is in power saving mode can be enabled or disabled byusing the parameters disclosed in the present invention. Morespecifically, whether to enable/disable can be represented in a bitmapform at the time when the MS enters power saving mode. Here, a pluralityof events can be enabled or disabled as a group. In the embodiments ofthe present invention represent examples where the plurality of eventsis enabled.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1-22. (canceled)
 23. A method for supporting a sleep mode action of amobile station (MS) in a wireless mobile communication system, themethod comprising: receiving, by the MS from a base station (BS), afirst message comprising trigger information, wherein the triggerinformation comprise at least one trigger condition and at least oneevent action which is performed upon reaching the at least one triggercondition; transmitting, by the MS to the BS, a sleep request message(MOB_SLP-REQ) comprising a first enabled triggered parameter whichcomprises a first bitmap indicating whether the at least one eventaction is enabled; receiving, by the MS from the BS, a sleep responsemessage (MOB_SLP-RSP) comprising a second enabled triggered parameterwhich comprises a second bitmap indicating whether the at least oneevent action is permitted; and performing the at least one event actionindicated by the second enabled triggered parameter when the at leastone trigger condition is reached, wherein the first bitmap comprisesbit#0 related to a scan report action, bit#1 related to a handoverrequest action and bit#2 related to a scan request action, and whereinthe second bitmap comprises bit#0 related to a scan report action, bit#1related to a handover request action and bit#2 related to a scan requestaction.
 24. The method according to claim 23, wherein the at least onetrigger condition is defined as at least one of Carrier-to-Interferenceand Noise Ratio (CINR), a Received Signal Strength Indicator (RSSI), anda Round Trip Delay (RTD).
 25. The method according to claim 24, whereinthe trigger information further comprises a function field defining acomputation method of the at least one of the trigger condition.
 26. Themethod according to claim 23, wherein the first message is a DownlinkChannel Descriptor (DCD) message or a Neighbor Advertisement(MOB_NBR-ADV) message.
 27. The method according to claim 23, whereineach of bits of the second bitmap is set to 1 to indicate the at leastone event action corresponding to the each of the bits are permitted.28. A mobile station (MS) for supporting a sleep mode action in awireless mobile communication system, wherein the MS is configured to:receive, from a base station (BS), a first message comprising triggerinformation, wherein the trigger information comprise at least onetrigger condition and at least one event action which is performed uponreaching the at least one trigger condition; transmit, to the BS, asleep request message (MOB_SLP-REQ) comprising a first enabled triggeredparameter which comprises a first bitmap indicating whether the at leastone event action is enabled; receive, from the BS, a sleep responsemessage (MOB_SLP-RSP) comprising a second enabled triggered parameterwhich comprises a second bitmap indicating whether the at least oneevent action is permitted; and performing the at least one event actionindicated by the second enabled triggered parameter when the at leastone trigger condition is reached, wherein the first bitmap comprisesbit#0 related to a scan report action, bit#1 related to a handoverrequest action and bit#2 related to a scan request action, and whereinthe second bitmap comprises bit#0 related to a scan report action, bit#1related to a handover request action and bit#2 related to a scan requestaction.
 29. The mobile station according to claim 28, wherein the atleast one trigger condition is defined as at least one ofCarrier-to-Interference and Noise Ratio (CINR), a Received SignalStrength Indicator (RSSI), and a Round Trip Delay (RTD).
 30. The mobilestation according to claim 29, wherein the trigger information furthercomprises a function field defining a computation method of the at leastone of the trigger condition.
 31. The mobile station according to claim28, wherein the first message is a Downlink Channel Descriptor (DCD)message or a Neighbor Advertisement (MOB_NBR-ADV) message.
 32. Themobile station according to claim 28, wherein each of bits of the secondbitmap is set to 1 to indicate the at least one event actioncorresponding to the each of the bits are permitted.
 33. A method forsupporting a sleep mode action of a mobile station (MS) in a wirelessmobile communication system, the method comprising: transmitting, by abase station (BS) to the MS, a first message comprising triggerinformation, wherein the trigger information comprise at least onetrigger condition and at least one event action which is performed uponreaching the at least one trigger condition; receiving, by the BS to theMS, a sleep request message (MOB_SLP-REQ) comprising a first enabledtriggered parameter which comprises a first bitmap indicating whetherthe at least one event action is enabled; and transmitting, by the BS tothe MS, a sleep response message (MOB_SLP-RSP) comprising a secondenabled triggered parameter which comprises a second bitmap indicatingwhether the at least one event action is permitted; wherein the at leastone event action indicated by the second enabled triggered parameter isperformed when the at least one trigger condition is reached, whereinthe first bitmap comprises bit#0 related to a scan report action, bit#1related to a handover request action and bit#2 related to a scan requestaction, and wherein the second bitmap comprises bit#0 related to a scanreport action, bit#1 related to a handover request action and bit#2related to a scan request action.
 34. The method according to claim 33,wherein the at least one trigger condition is defined as at least one ofCarrier-to-Interference and Noise Ratio (CINR), a Received SignalStrength Indicator (RSSI), and a Round Trip Delay (RTD).
 35. The methodaccording to claim 34, wherein the trigger information further comprisesa function field defining a computation method of the at least one ofthe trigger condition.
 36. The method according to claim 33, wherein thefirst message is a Downlink Channel Descriptor (DCD) message or aNeighbor Advertisement (MOB_NBR-ADV) message.
 37. The method accordingto claim 33, wherein each of bits of the second bitmap is set to 1 toindicate the at least one event action corresponding to the each of thebits are permitted.
 38. A base station (BS) for supporting a sleep modeaction of a mobile station (MS) in a wireless mobile communicationsystem, wherein the BS is configured to: transmit, to the MS, a firstmessage comprising trigger information, wherein the trigger informationcomprise at least one trigger condition and at least one event actionwhich is performed upon reaching the at least one trigger condition;receive, to the MS, a sleep request message (MOB_SLP-REQ) comprising afirst enabled triggered parameter which comprises a first bitmapindicating whether the at least one event action is enabled; andtransmit, to the MS, a sleep response message (MOB_SLP-RSP) comprising asecond enabled triggered parameter which comprises a second bitmapindicating whether the at least one event action is permitted; whereinthe at least one event action indicated by the second enabled triggeredparameter is performed when the at least one trigger condition isreached, wherein the first bitmap comprises bit#0 related to a scanreport action, bit#1 related to a handover request action and bit#2related to a scan request action, and wherein the second bitmapcomprises bit#0 related to a scan report action, bit#1 related to ahandover request action and bit#2 related to a scan request action. 39.The base station according to claim 38, wherein the at least one triggercondition is defined as at least one of Carrier-to-Interference andNoise Ratio (CINR), a Received Signal Strength Indicator (RSSI), and aRound Trip Delay (RTD).
 40. The base station according to claim 39,wherein the trigger information further comprises a function fielddefining a computation method of the at least one of the triggercondition.
 41. The base station according to claim 38, wherein the firstmessage is a Downlink Channel Descriptor (DCD) message or a NeighborAdvertisement (MOB_NBR-ADV) message.
 42. The base station according toclaim 38, wherein each of bits of the second bitmap is set to 1 toindicate the at least one event action corresponding to the each of thebits are permitted.